Receptors for transplantation antigens may be visualized directly on unsensitized cells with the use of an anti-idiotypic antisera. It should be possible to eliminate these cells specifically by adherence to a cellular immunoadsorbent or by treatment of the unsensitized population with sera directed at the specific binding site. Alternatively, active and continuing control of the cells reactive to specific transplantation antigens may be possible with suppressor cells specific for the binding site. Immunoadsorption using spleen cell monolayers is highly efficient and specific in removal of cytotoxic cells from a sensitized population but is not effective in removing precursors of these cells. Antisera with the capacity to inhibit in vitro generation of cytotoxic cells have been raised. To date, activity of these sera has been too low to permit clear conclusions about specificity of the inhibition. Suppressor cells have also been generated. These cells have the property of inhibiting the in vitro generation of cytotoxic cells and in some experiments appear to be specific. Clear interpretation has been hindered by the substantial nonspecific augmenting properties these suppressor populations also possess. BIBLIOGRAPHIC REFERENCES: Neefe, J. R., and Sachs, D. H.: Specific elimination of cytotoxic cells. II. Reduction of cytotoxic activity by adsorption on monolayers results from removal of cytotoxic cells and not from inhibition of their activity. Cell. Immunol. 29: 129-136, 1977. Neefe, J. R., and Sachs, D. H.: Adherence properties of cytotoxic cells and their precursors on spleen cell monolayers. Transplant. Proc. 9: 797-799, 1977.